Mechanical and chemical-mechanical planarizing processes (collectively "CMP") are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays, and many other microelectronic-device substrates and substrate assemblies. FIG. 1 is a partially schematic isometric view of a conventional web-format planarizing machine 10 that has a platen 20. A sub-pad 50 is attached to the platen 20 to provide a flat, solid workstation for supporting a portion of a web-format planarizing pad 40 in a planarizing zone "A" during planarization. The planarizing machine 10 also has a pad-advancing mechanism, including a plurality of rollers, to guide, position, and hold the web-format pad 40 over the sub-pad 50. The pad-advancing mechanism generally includes a supply roller 24, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. As explained below, a motor (not shown) drives the take-up roller 23 to advance the pad 40 across the sub-pad 50 along a travel path T-T. The motor can also drive the supply roller 24. The first idler roller 21a and the first guide roller 22a press an operative portion of the pad 40 against the sub-pad 50 to hold the pad 40 stationary during operation.
The planarizing machine 10 also has a carrier assembly 30 to translate a substrate 12 over the polishing pad 40. In one embodiment, the carrier assembly 30 has a head 31 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. The carrier assembly 30 also has a support gantry 34 and a drive assembly 35 that can move along the gantry 34. The drive assembly 35 has an actuator 36, a driveshaft 37 coupled to the actuator 36, and an arm 38 projecting from the driveshaft 37. The arm 38 carries the head 31 via a terminal shaft 39. The actuator 36 orbits the head 31 about an axis B--B (as indicated by arrow R1) and can rotate the head 31 (as indicated by arrow R.sub.2) to move the substrate 12 over the polishing pad 40 while a planarizing fluid 43 flows from a plurality of nozzles 45 in the head 31. The planarizing fluid 43 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the substrate 12, or the planarizing fluid 43 may be a non-abrasive planarizing solution without abrasive particles. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed-abrasive polishing pads.
In the operation of the planarizing machine 10, the polishing pad 40 moves across the sub-pad 50 along the travel path T--T either during or between planarizing cycles to change the particular portion of the polishing pad 40 in the planarizing zone A. For example, the supply and take-up rollers 24, 23 can drive the polishing pad 40 between planarizing cycles such that a point P moves incrementally across the sub-pad 50 to a number of intermediate locations I.sub.1, I.sub.2, etc. Alternatively, the rollers 24, 23 may drive the polishing pad 40 between planarizing cycles such that the point P moves all the way across the sub-pad 50 to completely remove a used portion of the polishing pad 40 from the planarizing zone A. The rollers 24, 23 may also continuously drive the polishing pad 40 at a slow rate during a planarizing cycle such that the point P moves continuously across the sub-pad 50 during planarization. In any case, the motion of the polishing pad 40 is generally relatively slow when the substrate 12 engages the polishing pad 40 and the relative motion between the substrate 12 and the polishing pad 40 is primarily due to the motion of the head 31.
One drawback with the apparatus shown in FIG. 1 is that debris can become caught between the polishing pad 40 and the sub-pad 50. The debris can cause a local bump or other non-uniformity in the polishing pad 40 which can create a corresponding non-uniformity in the substrate 12 and/or can cause the polishing pad 40 to wear in a non-uniform manner.
A further drawback is that the polishing pad 40 can adhere to the sub-pad 50 during planarization. This adhesive bond must be broken in order to advance the polishing pad 40. In one conventional method, the idler rollers 21a, 21b and/or the guide roller 22a are actuated to move the polishing pad 40 normal to the upper surface of the sub-pad 50 and break the adhesive bond. However, moving the polishing pad 40 normal to the sub-pad 50 can flex the polishing pad 40 and cause cracks, pits, and other defects to form in the polishing pad 40, which can in turn create non-uniformities in the planarized surface of the substrate 12.
Another drawback is that the polishing pad 40 and the sub-pad 50 can wear or abrade as they rub against each other. Accordingly, the polishing pad 40 and the sub-pad 50 may need to be replaced on a frequent basis and/or the polishing pad 40 may develop non-uniformities.
One conventional CMP apparatus which may address some of the foregoing drawbacks includes a polishing pad that forms a continuous loop and that moves a high speed relative to the substrate, in the manner of a belt sander. FIG. 2 is a partially schematic side elevation view of one such conventional CMP apparatus 10a having a continuous polishing pad 40a extending around two rollers 25. The polishing pad 40a can be supported by a continuous support band 41, formed from a flexible material, such as a thin sheet of stainless steel. A pair of platens 20a provide additional support for the polishing pad 40a at two opposing planarizing stations. Two carriers 30a, each aligned with one of the platens 20a can each bias a substrate 12 against opposing outwardly-facing portions of a planarizing surface 42a of the polishing pad 40a. Devices such as the apparatus 10a shown in FIG. 2 and having vertically oriented planarizing stations are available from Aplex, Inc. of Sunnyvale, Calif. under the name AVERA.TM.. Generally similar devices having a horizontally-oriented polishing pad 40a and a single carrier 30a are available from Lam Research Corporation of Fremont, Calif.
During operation, the continuous polishing pad 40a moves at a relatively high speed around the rollers 25 while the carriers 30a press the substrates 12 against the polishing pad 40a. An abrasive slurry is introduced to the planarizing surface 42a of the polishing pad 40a so that the slurry, in combination with the motion of the polishing pad 40a relative to the substrates 12, mechanically removes material from the substrates 12.
One drawback with the apparatus 10a shown in FIG. 2 is that the polishing pad 40a must move at a high speed to effectively planarize the substrates 12. The high-speed polishing pad 40a can present a safety hazard to personnel positioned nearby, for example, if the polishing pad 40a should break, loosen, or otherwise malfunction during operation.
Another drawback is that the combination of the polishing pad 40a and the support band 41 may also wear more quickly than other polishing pads because both the planarizing surface 42a of the polishing pad 40a and a rear surface 44 of the support band 41 rub against relatively hard surfaces (i.e., the polishing pad 40a rubs against the substrate 12 and the support band 41 rubs against the platen 20a). This drawback can be serious because, once a defect forms in the polishing pad 40a, it can affect each subsequent substrate 12.
Still another drawback is that the interface between the support band 41 and the platens 20a can be difficult to seal, due to the high speed of the support band 41. Accordingly, the abrasive slurry can seep between and abrade the support band 41 and the platens 20a.